Patent GB-697918-A (GB)
Title: Apparatus for the electrostatic precipitation of solid and liquid particles from a gas-flow
IPC: B03C3/38
Filed: 1950-12-22
Abstract: 697,918. Electrostatic filters. SOC. FINANCIERE D'EXPANSION COMMERCIALE ET INDUSTRIELLE SOC. ANON. SFINDEX. Dec. 22,1950 [Feb. 22, 1950], No. 31277/50. Class 39(i) In an apparatus for the electrostatic precipitation of solid and liquid particles from a gas flow, sources of radio-active radiation are provided for causing the ionization of the gas molecules for the purpose of electric charging the solid and liquid particles contained in the gas flow, said sources at least partially being arranged near the inlet of a system of electrodes, through which the gas flow passes, connected to a source of potential which produces an electric field transverse to the direction of the gas flow so that the solid and liquid particles of the gas flow are diverted transverse to the gas flow and precipitate on the electrodes, the intensity of the field being such that spark or glow discharges are avoided. In one embodiment, Fig. 3, the gas flow enters at 15 and is led to the electrode system by way of a duct 16 having a ring 22 of radio-active substances on its inner surface. The electrode system comprises a cylindrical outer electrode 17 supported by insulating rings 18 and 19 and connected to the negative terminal 25 of an H.T. source 26, and a tubular inner electrode 20 connected to the positive terminal 27 of the source 26 and thereby to the frame of the apparatus. Flushing liquid entering at 29 through a valve 30 controlled by an electrical device 31 is ejected through perforations 28 in the inner electrode 20 and is collected in a hopper 32, finally leaving the apparatus at 33 through a valve 34 having an electrical control device 35. A control device 36 cuts off the H.T. and opens the valve 34 when the inlet valve 30 is opened, while a timing device ensures that the valve 34 is closed and the H.T. connected again after expiry of the time necessary for drying the apparatus after flushing. The gas flow on its exit from the electrode system is diverted in a housing 23 and leaves the apparatus at 24. The radio-active substance. 5, Fig. 2, is applied to a strip 10 by an electrolytic process or other method, leaving a non-active border along both edges, and is covered by a thin layer 13, for example gold foil, which is either rolled on to the strip 10 or fixed to it electrolytically to prevent the passage of the radon gas evolved by the decomposition of the radio-active material. If radium is used additional lead screening is necessary. In cases where the radial distance between the electrodes 17 and 20 is greater than the range, in the gas under purification, of the alpha particles emitted by the radioactive material, the radio-active layer is placed at 22a on the inner surface of the electrode 17 so that it lies in the electric field between the electrodes and an ion current develops to effect the electric charging of the particles in the gas flow. Alternatively, the radio-active substance may be placed on the outer surface of the inner electrode. A number of precipitators may be arranged and operated in parallel to deal with large gas volumes. Valuable substances contained in air or gas currents in the form of dust or mist may be separated and recovered by using suitable flushing liquids. The live electrodes and conductors may be provided with a gas-tight coating of insulating material to allow the precipitation of solid and liquid particles which are themselves combustible or are carried in explosive gases, or the electrodes may be metallic layers on the sides of insulating bodies remote from the gas flow so that metal dust may be precipitated. In an alternative embodiment, Fig. 6, the radio-active material 53a is placed on the inner face of a frame 52a and the electrode system comprises a series of metal tubes 54a, 55a of rectangular cross-section. Alternatively, the electrodes may be tubes of circular cross-section or flat plates. The frame itself may form the outer electrode in which case the inner electrode is a plate mounted inside the frame and the radio-active material may then be placed on this inner electrode. A two-field type of precipitator is described in which radio-active material is applied to the down-stream electrodes of the ionizing field to produce an ion current flowing in the opposite direction to the gas flow, so that the gas remains in the ionization region for an extended period.